Process for dewaxing oils



Patented July 28, 1936 PROCESS FOR DEWAXING OILS poration of Delaware No Drawing. Application October 18, 1933,

Serial No. 694,038 r 6 Claims.

This invention relates to a process of dewaxing petroleum oils, specially lubricating oils, in which the wax may be present in the form of crystalline wax or in the form of a wax which is substantially amorphous. The present process is more especially adapted to remove from petroleum oils Waxes which are too crystalline for satisfactory removal by cold settling or centrifuging and which are so contaminated with amorphous wax that they are not readily removed by ordinary filter pressing. The wax bearing petroleum oils may be derived from natural crudes or hydrogenated stocks and may be produced from them either as overhead distillates or as residual oils.

So called solvent dewaxing processes have been developed in the art of refining petroleum oils.

The wax bearing oil is dissolved in a one component or more component solvent and chilled whereby the wax is precipitated. Further steps consist of removing the precipitated wax from the oil solvent mixture by various methods such as cold settling, centrifuging, or filter pressing, and then removing the solvent from the oil by distillation.

According to the present invention, secondary butyl acetate is used as a solvent in dewaxing petroluem oils. This solvent has the great advantage of giving unusually high through-puts, that is, is for a given wax removing equipment, a large quantity of oil can be dewaxed in a day. It also has the second desirable characteristic of good solvents for dewaxing, consisting in that the differential between the dewaxing temperature and the pour point of the dewaxed oil is very little. Furthermore, its miscibility limitations do not prevent its economic use with heavier types of lubricating oils. Due to these desirable characteristics, secondary butyl acetate is an ideal one component solvent for the efficient and satisfactory removal of wax from hydrogenated or nonhydrogenated petroleum oils with or without the use of filter aid mediums.

Even though the use of secondary butyl acetate permits a very emcient dewaxing of petroleum oils, its efiiciency can be increased by the addition of a second component which may or may not decrease the solubility of the wax in the oil solution. This second component while seldom giving dewaxed oil of a lower pour point, has a very marked elfect on increasing the through-put per a given dewaxing equipment in unit time. I am unable to offer a satisfactory explanation at the present time for this behavior of secondary butyl acetate when used in conjunction with another solvent. Such solvent components which may be added to advantage to secondary butyl acetate are primary aliphatic alcohols including methyl, ethyl, propyl, butyl, amyl and hexyl alcohol, etc., or the secondary and tertiary alcohols such as iso-propyl alcohol, ketones such as acetone, certain halogenated hydrocarbons such as ethylene dichloride, etc.

The temperature to which the oil-solvent mixture is cooled for the precipitation of the wax depends on the pour point required from the dewaxed oil and may vary within broad limits.

The following mixtures prove to be especially advantageous for dewaxing petroleum oils:

Secondary butyl acetate -95% by volumeacetone 35-5% Secondary butyl acetate -90% iso-propyl alcohol 25-10% Secondary butyl acetate 1 l0% ethylene dichloride 99-60% Secondary butyl acetate 70-95% secondary butyl alcohol 30-5% Secondary butyl acetate 50-90% secondary amyl alcohol 50-10% The following examples will serve to illustrate the invention.

Thirty-five parts of a residual cylinder stock having a viscosity of 135 seconds Saybolt at 210 F. and a pour point of F. were blended with 65 parts of secondary butyl acetate. The mixture was heated to 110 F. to insure complete miscibility of the wax. After charging to the blow cases connected with a closed type rotary press, the solution was chilled with constant stirring at the rate of 5 F. per hour to a pressing temperature of 0 F. Filter aid was then added in an amount equaling 50 lbs. per gallons of stock and the chilled mixture admitted to the press and filtered under 50 lbs. pressure per square inch at a rate of 454 barrels of dewaxed oil per day per 720 square feet of filter surface. The dewaxed oil had a pour point of 10 F.

In another experiment a solvent consisting of 88% secondary butyl acetate and 12% iso-propyl alcohol was used for dewaxing the same residual cylinder stock, thirty-five parts by volume of which were blended with 65 parts of the solvent mixture. Under identical operating conditions as in the previous example, the through-put was increased to 730 barrels per day of dewaxed oil of 10 F. pour.

The present invention is not to be limited by the examples or by the particular details disclosed for the purpose of better understanding of the process but only by the following claims in which it is my intention to claim all novelty inherent in the invention.

What I claim is:

1. The process of dewaxing pertroleum oil which comprises admixing the oil with an oilsolvent comprising an efiective amount of secondary butyl acetate, chilling the oil solvent mixture to precipitate the wax, and. separating the precipitated wax.

2. The process of dewaxing petroleum oil which comprises admixing the oil with a multiple component solvent mixture, one component of which is an effective amount of secondary butyl acetate, chilling the oil solvent mixture, and separating the precipitated wax.

3. The process of dewaxing petroleum oil which comprises admixing the oil with an oil-solvent comprising an effective amount of secondary butyl acetate and a normally liquid aliphatic alcohol, chilling the mixture to precipitate the wax, and separating the precipitated wax.

4. The process of dewaxing petroleum oil which comprises admixing the oil with an oil-solvent comprising approximately 75-90% by volume of secondary butyl acetate and -10% by volume of isopropyl alcohol, chilling the mixture and separating the precipitated wax.

5. The process of dewaxing petroleum oil which comprises admixing the oil with an oil-solvent comprising an effective amount up to by volume of secondary butyl acetate and at least by volume of ethylene dichloride, chilling the mixture to precipitate the wax and separating the precipitated wax.

6. Process of dewaxing petroleum oil which comprises admixing the oil with an oil-solvent comprising -95% secondary butyl acetate and 35-25% acetone.

ARTHUR M. WILSON. 

